1. Field of the Invention
The present invention relates to accumulators and regulators. In particular, the present invention relates to accumulators and regulators that may be implemented in pressurized fluidic conditions or where remote hydraulic control of a regulator is required.
2. Description of Related Art
This invention preferably may be used for deepwater accumulators that supply pressurized fluid to control and operate equipment disposed below fluid levels.
Accumulators are typically associated with blowout preventers (BOP) in order to temporarily cease well bore operations, gate valves in order to control fluid flow and to divert various fluids to surfaces or other subsea locations, as well as hydraulically actuated connectors and similarly associated devices. Pressurized fluid is typically an oil or water based fluid with increased lubricity and corrosion protection.
Currently accumulators come in various styles, but most share the same underlying operative principle. This principle involves pre-charging each accumulator with pressurized gas to a pressure which closely approximates the minimally anticipated operative pressure, which often approaches the ambient temperature of the environment in which the accumulator will be used. By pre-charging an accumulator fluid may be optionally added to the accumulator, increasing the pressure of the pressurized gas and the fluid. Fluid introduced into the accumulator is therefore stored at a pressure at least as high as the pre-charged pressure and is capable of doing hydraulic work.
Accumulators are often styled to operate in a bladder, piston, or float type fashion. Bladder types open employ an expandable bladder which separates gasses from fluids. Piston types use a piston which translates along an axis to separate fluids from gasses. Float types use a float to provide a partial separation of fluid from gas and closing of a valve when the float approaches the bottom. This in turn prevents the escape of gas.
Pilot Accumulators are typically pre-charged with gas at approximately ambient pressure plus the minimum working pressure of the circuit. As accumulators are used in deeper water, the efficiency of conventional accumulators is decreased. In 1000 feet of seawater ambient pressure approximates 465 pounds per square inch. Thus, in order for an accumulator to provide a 500 psi differential at 1000 ft. depth, it is required to be pre-charged at 732.5 pounds per square inch. At about 4000 feet of depth, ambient pressure is approximates 930 pounds per square inch, requiring an initial pre-charge of 1430 pounds per square inch, when only 500 pounds per square inch is required for operations. And at 10,000 ft, these numbers are 4,650 plus 500 psi. This is problematic because cylindrical design often requires thicker walls, stronger end caps, tighter welds, and stronger materials merely to accomplish an operative working environment. When higher working pressures are employed, larger deviations in translational pressure shifts occur. This requires stronger sealing mechanisms and more accurate gauges. When pressure variants are introduced into the environment, often being cold water, even more extraneous pressure is required to get an accumulator to operational status. For example subsea accumulators are often exposed to very cold temperatures after being pre-charged which causes them to lose pressure.
As the BOP is deployed, the ambient pressure increases, thus decreasing the efficiency of the gas accumulators and can render them useless and cause the system to lose functionality. To alleviate this problem, the current approach is to fit multiple parallel accumulators into the circuit with multiple pre-charge pressures to allow added control at different depths.
The use of these multiple accumulators adds another problem, as the rates of increase and decrease vary with the volume of gas contained in the system, thus making control erratic and changing dependent on the depth. Also as deployment takes place, the isolated fluid in the system loses pressure equal to the increase of the ambient pressure, requiring frequent adjustments to the internal pressure to keep the system within the control range required to operate the functions.
Due to the properties of the gas systems, increasing the pressure is not linear and follows a parabolic arc, thus limiting control at higher pressures.
Although these systems represent great strides in the area of accumulator technology, many shortcomings remain.
Thus there exists a need for an accumulator that is capable of operating at a higher pressure and not required to be overly pre-charged with pressure, not require multiple pre-charge pressures and not require frequent pressure increases during deployment and conversely, not require frequent decreases during recovery. Without decreases during recovery, due to error or equipment failure, the internal pressure at the surface can be as high as 3,000 psi plus the ambient pressure due to water depth. At 10,000 feet this could be 7,650 psi.